Optical dielectric waveguide structure

ABSTRACT

An optical subassembly includes a planar dielectric waveguide structure that is deposited at temperatures below 400 C. The waveguide provides low film stress and low optical signal loss. Optical and electrical devices mounted onto the subassembly are aligned to planar optical waveguides using alignment marks and stops. Optical signals are delivered to the submount assembly via optical fibers. The dielectric stack structure used to fabricate the waveguide provides cavity walls that produce a cavity, within which optical, optoelectronic, and electronic devices can be mounted. The dielectric stack is deposited on an interconnect layer on a substrate, and the intermetal dielectric can contain thermally conductive dielectric layers to provide pathways for heat dissipation from heat generating optoelectronic devices such as lasers.

FIELD OF THE INVENTION

The present invention relates to optoelectronic communication systems,and more particularly to a planar waveguide structure. Opticaldielectric interposers are formed from the integration and patterning ofthis planar waveguide structure with a substrate to form compactinterposers and optical sub mount assemblies that provide low loss inoptoelectronic packages that are used for optical signal routing andtransmission.

BACKGROUND

Waveguides are used in optical communication networks for thetransmission and routing of optical signals. For the transmission of theoptical signals over long distances, waveguides can take the form ofoptical fibers, thin strands of glass that are used to transfer dataover distances that can span tens of kilometers without a repeater.Within the networks of long range optical fibers are signal processingnodes that contain packaged photonic and optoelectronic circuits thatare used to perform various functions such as to encode, send, receive,decode, multiplex, and de-multiplex, among other optical and electricalsignal processing functions, the optical signals that are delivered tothese processing nodes via the optical fibers. And within theoptoelectronic circuits in these processing nodes, optical signals aretransmitted via free space and through short lengths of waveguide. Theseshort lengths of waveguide are used to guide signals to a variety ofsmall packaged devices or components that can transfer, combine, split,and route optical signals as the demands of the network require.

Routing of optical signals from the optical fibers to components on thesub mount assembly have historically been accomplished via transmissionin free space, and to some extent, via planar optical waveguides on thesub mount assembly. Optical transmission in free space can requirelenses to focus and direct the optical signals between components in theoptical circuits and can require large spatial volumes to accommodatethese lenses, which can lead to undesirably large package sizes forthese optical circuits. Additionally, the transmission of the signals infree space can result in significant signal losses from uncontrolledscattering and reflection. Alternatively, planar optical waveguidesoffer the potential for significant reduction in optoelectronic packagesize. The integration and patterning of planar waveguide structures onsubstrates allow for the transmission and distribution of opticalsignals without the need for large discrete optical components.Integrated waveguide structures also allow for the formation of opticaldevice structures, such as filters, gratings, and spot size converters,for example, directly onto the substrate.

Optoelectronic packages at signal processing nodes in opticalcommunications networks generally include an optical sub mount assembly,which typically consists of one or more optical die (such as lasers andphotodetectors), and that can include either the means for the freespace transmission of optical signals or the planar waveguides andassociated optical routing components, all of which are enclosed in anhermetically-sealed cavity formed by a cap and a substrate. A sub mountassembly can include, for example. a substrate or interposer, theoptical routing components, and the signal-generating andsignal-receiving devices and components. The planar waveguide structuresare deposited and patterned to form waveguides and optical devicecomponents, or in some applications, added as discrete elements.Currently, the capability for fabricating planar waveguide structures ofsufficient thickness with low stress is limited, and therefore, a needexists in the art of optoelectronic packaging for a planar waveguidestructure that can be deposited onto a substrate, and from which compactand economical interposers and sub mount assemblies can be formed. Thus,there is a need in the art for a planar optical waveguide structure fortransmission and routing of optical signals in photonic integratedcircuits that has low optical loss, has low stress, is compact, and iseconomically manufacturable.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments of systems,methods, and other aspects of the invention. It will be apparent to aperson skilled in the art that the illustrated element boundaries (e.g.,boxes, groups of boxes, or other shapes) in the figures represent oneexample of the boundaries. In some examples, one element may be designedas multiple elements, or multiple elements may be designed as oneelement. In some examples, an element shown as an internal component ofone element may be implemented as an external component in another, andvice versa.

Various embodiments of the present invention are illustrated by way ofexample, and not limited by the appended figures, in which likereferences indicate similar elements, and in which:

FIG. 1A shows cross-sectional schematic views of the inventivedielectric film structure for the formation of integrated planarwaveguide structures;

FIG. 1B shows a cross-sectional view of a single or multilayerdielectric top spacer layer structure for the inventive planardielectric waveguide structure;

FIG. 1C shows a cross-sectional view of a multilayer, repeating siliconoxynitride film structure for the inventive planar dielectric waveguidestructure;

FIG. 1D shows a cross-sectional view of a single or multilayerdielectric bottom spacer layer structure for the inventive planardielectric waveguide structure;

FIG. 2A-2B show measured film stress in accordance with embodiments for(A) dielectric films deposited at various film thicknesses, and (B)dielectric films of various refractive indexes;

FIG. 3A-3B show measured optical losses in accordance with embodimentsfor (A) dielectric films of various refractive indexes and (B)dielectric waveguide film structures with various bottom buffer layerfilm thicknesses;

FIG. 4A-4C show steps for forming some embodiments of the inventivedielectric film structure (A) at low temperature and having low stressand low optical loss, (B) with each dielectric film deposited at lowtemperature and having low stress and low optical loss, and (C) thatinclude a substrate with a buffer layer, one or more optional bottomspacer layers, a repeating stack of one or more dielectric layers, oneor more optional top spacer layers, and an optional top layer, followedby pattering of the stack to form a waveguide;

FIG. 5A-5B show cross sectional schematic views of embodiments of anintegrated planar waveguide on a substrate: (A) withoutoptical/electrical devices, and (B) with optical/electrical devices;

FIG. 6A-6B show cross sectional schematic views of embodiments ofintegrated planar waveguides on a substrate with an interconnect layerin accordance with the inventive process: (A) without optical/electricaldevices and (B) with optical/electrical devices;

FIG. 7A-7B show cross sectional schematic views of embodiments ofintegrated planar waveguides on a substrate with interconnect layer andintegrated electrical devices in the substrate in accordance with theinventive process: (A) without surface mounted optical or electricaldevices and (B) with surface mounted optical or electrical device;

FIG. 8A-8B show cross sectional schematic views of embodiments ofintegrated planar waveguides on a substrate with interconnect layer andintegrated electrical devices in the substrate in accordance with theinventive process shown with interconnections between top surfacemounted device and integrated electrical devices in the substrate: (A)shown without the top mounted optical or electrical devices in place,and (B) with top mounted optical or electrical device; also shown is theposition of an optical fiber relative to the planar waveguide in anembodiment;

FIG. 9A-9D show cross sectional schematic views of embodiments of asubstrate with interconnect layer: (A) with inventive dielectric stackmounted via bond pads to the substrate as a discrete optical waveguidecomponent, (B) with inventive dielectric stack mounted to the substrateas a discrete optical waveguide component and aligned with discreteoptical and electrical devices, and aligned to an optical fiber, (C)with inventive dielectric stack mounted to the substrate as a discreteoptical waveguide component, for which the substrate contains integratedelectrical devices, and (D) with inventive dielectric stack mounted tothe substrate as a discrete optical waveguide component and aligned withdiscrete optical and electrical devices, and aligned to an optical fiberfor an embodiment in which the substrate contains integrated electricaldevices;

FIG. 10A-10B show steps in the fabrication of embodiments of providing apatterned dielectric waveguide structure (A) on a substrate with one ormore integrated devices in the substrate that are coupled to aninterconnect layer, and (B) on a substrate with one or more integrateddevices in the substrate that are coupled to the inventive planarwaveguide through an interconnect layer and a device, and to an opticalfiber that is configured to interface with the planar waveguide;

FIG. 11A shows a perspective schematic view of a substrate withpatterned inventive dielectric waveguide structure, with a v-groove formounting and alignment of an optical fiber and with mechanical stops forthe mounting and alignment of optical and electrical devices and die,and FIG. 11B shows a cross sectional schematic view of embodiments ofintegrated planar waveguide structures on a substrate with alignmentmark and stops for alignment of optical/electrical devices;

FIG. 12 shows steps in the fabrication of embodiments of the inventivedielectric film structures for providing patterned dielectric waveguideson substrates with features for the alignment of optical and electricaldevices;

FIG. 13A-13B show cross sectional schematic views of embodiments ofintegrated planar waveguides on a substrate with integrated heat sinklayer (A) on the substrate, and (B) within the interconnect layer;

FIGS. 14A-14B show steps in the fabrication of embodiments of theinventive dielectric film structure for providing patterned dielectricwaveguide structures with (A) interconnection layer formed on a thermalconductive layer, and (B) a high thermal conductivity dielectric layerwithin the interconnect layer;

FIG. 15A-15D show a cross sectional schematic view of embodiments ofintegrated planar waveguides on a substrate shown (A) with unpatterneddielectric waveguide stack, (B) patterned dielectric waveguide structurewith resulting cavity shown in cross section and, in the inset, in aperspective view, (C) with patterned dielectric waveguide structure andwith mounted optical/electrical die within the cavity, and (D) withpatterned dielectric waveguide structure, mounted optical/electricaldie, and hermetic sealing cap;

FIG. 16 shows steps in the fabrication of embodiments of the inventivedielectric film structure for the formation of integrated planarwaveguides and mechanical support structures to support hermeticsealing.

SUMMARY

Embodiments of the present invention are directed to the fabrication ofintegrated planar dielectric waveguides that are formed and patternedprimarily on semiconducting or insulating substrates. The combination ofan integrated planar waveguide and a substrate, to form an opticaldielectric interposer, serves as a subcomponent of an optical sub mountassembly for an optoelectronic package.

The present invention is based, in part, on the development of adielectric waveguide structure that transmits optical signals with lowloss, is integrated into a substrate and thereby reduces fabricationcosts, is deposited at low processing temperatures of less than 400 C,and preferably less than 300 C, and is fabricated with low stress toprevent stress-induced delamination of the film structure anddeformation of the substrate. As further described herein, the inventionprovides superior optical and mechanical performance and providessuperior economic benefits in comparison to the current state of the art

In exemplary embodiments, planar dielectric film structures of multiplelayers of silicon oxynitride are formed on a substrate and patternedinto waveguides. The achievable waveguide thicknesses using theinventive film structure can produce optical losses that are typicallyless than 1 dB/cm and that exhibit post-deposition stress levels of lessthan 20 MPa.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided herein. It should beunderstood that the detailed description of exemplary embodiments isintended for illustration purposes only and is, therefore, not intendedto necessarily limit the scope of the present invention.

DETAILED DESCRIPTION

The ensuing description provides exemplary embodiment(s) only, and isnot intended to limit the scope, applicability or configuration of thedisclosure. Rather, the ensuing description of the exemplaryembodiment(s) will provide those skilled in the art with an enablingdescription for implementing an exemplary embodiment. It beingunderstood that various changes may be made in the function andarrangement of elements without departing from the spirit and scope asset forth in the appended claims.

An “interposer” as used herein and throughout this disclosure refers to,but is not limited to, a substrate that provides mechanical support andelectrical or optical interface routing from one or more electrical,optical, and optoelectrical devices to another. Interposers aretypically used to route optical or electrical connections from variousdevices or die that are mounted on, or connected to, the interposer. An“optical interposer” is an interposer that provides for the opticalinterfacing between optical devices mounted or connected thereon.

A “sub mount assembly” as used herein and throughout this disclosurerefers to, but is not limited to, an assembly that includes a substrate,typically an interposer, that is populated with one or more optical,optoelectrical, and electrical devices.

A “substrate” as used herein and throughout this disclosure refers to,but is not limited to, a mechanical support upon which an interposer isformed. Substrates may include, but not be limited to, silicon, indiumphosphide, gallium arsenide, silicon, silicon oxide-on-silicon, silicondioxide-on-silicon, silica-on-polymer, glass, a metal, a ceramic, apolymer, or a combination thereof. Substrates may include asemiconductor or other substrate material, and one or more layers ofmaterials such as those used in the formation of an interconnect layer.

An “optical die” as used herein and throughout this disclosure refersto, but is not limited to, a discrete optical device such as a laser orphotodetector that can be positioned into a sub mount assembly as acomponent of an optical or optoelectronic circuit.

An “optoelectronic package” as used herein and throughout thisdisclosure refers to, but is not limited to, an assembly that istypically hermetically sealed, and that typically includes a sub mountassembly and a cap; the package typically provides electrical, optical,or both electrical and optical interconnects for combining with externaloptoelectronic, electronic, and optical components as in, for example,an optical communications network, an optical circuit, or an electricalcircuit.

An “optical waveguide” as used herein and throughout this disclosurerefers to, but is not limited to, a medium for transmitting opticalsignals.

“Optical signals” as used herein and throughout this disclosure refersto, but is not limited to, electromagnetic signals typically in theinfrared and visible light ranges of the electromagnetic spectrum thatare encoded with information.

A “semiconductor” as used herein and throughout this disclosure refersto, but is not limited to, a material having an electrical conductivityvalue falling between that of a conductor and an insulator. The materialmay be an elemental material or a compound material. A semiconductor mayinclude, but not be limited to, an element, a binary alloy, a tertiaryalloy, and a quaternary alloy. Structures formed using a semiconductoror semiconductors may include a single semiconductor material, two ormore semiconductor materials, a semiconductor alloy of a singlecomposition, a semiconductor alloy of two or more discrete compositions,and a semiconductor alloy graded from a first semiconductor alloy to asecond semiconductor alloy. A semiconductor may be one of undoped(intrinsic), p-type doped, n-typed doped, graded in doping from a firstdoping level of one type to a second doping level of the same type, andgraded in doping from a first doping level of one type to a seconddoping level of a different type. Semiconductors may include, but arenot limited to III-V semiconductors, such as those between aluminum(Al), gallium (Ga), and indium (In) with nitrogen (N), phosphorous (P),arsenic (As) and tin (Sb), including for example GaN, GaP, GaAs, InP,InAs, AlN and AlAs.

“Silicon oxynitride” as used herein and throughout this disclosurerefers to, but is not limited to, a dielectric material that is formedby a combination of constituent elements of silicon, oxygen, andnitrogen. In some instances, the term “silicon oxynitride” can refer tosilicon oxides and silicon nitrides in the general sense that siliconoxides and silicon nitrides are silicon oxynitrides with very low orinsignificant levels of either the nitrogen in the case of siliconoxides, and oxygen in the case of silicon nitrides. Film properties,such as the refractive index, can be controlled or varied by varying theconcentrations and the ratios of the constituent elements of silicon,oxygen, and nitrogen, and to some extent, by the concentrations ofimpurities in the films. The removal of nitrogen or the reduction ofnitrogen to low levels, for example, in one film of a film stack, doesnot change the designation of the material as silicon oxynitride withinthe context of this disclosure. Similarly, the removal of oxygen or thereduction of oxygen to very low levels does not change the designationof the resulting material as a silicon oxynitride. Materials with low orunmeasurable levels of either nitrogen or oxygen should, therefore, beviewed as silicon oxynitrides within the context of this disclosure. Theratio of silicon to oxygen to nitrogen in silicon oxynitride films canvary over a wide range and variations in the ratio of these constituentelements can lead to variations in the refractive indices of siliconoxynitride films as described herein. The concentrations of impuritiesin the films, from the deposition processes used to form the films, canalso influence the indices of refraction of the silicon oxynitridefilms. Silicon oxynitride is electrically insulating and opticallytransparent.

“Silicon oxide” as used herein and throughout this disclosure refers to,but is not limited to, a dielectric material that is formed from acombination of silicon and oxygen, and in some instances may containother elements such as hydrogen, for example, as a byproduct of thedeposition method. In its most common form, the ratio of oxygen tosilicon is 2:1 (silicon dioxide) but variations in this ratio remainwithin the scope of the definition of silicon oxide as used for thesilicon oxide films in this disclosure. Similarly, variations instoichiometry are to be anticipated and applicable for filmsspecifically referred to in this disclosure as silicon dioxide.

“Silicon nitride” as used herein and throughout this disclosure refersto, but is not limited to, a dielectric material that is formed from acombination of silicon and nitrogen, and in some instances may containother elements such as hydrogen, for example, as a byproduct of thedeposition method. In its most common form, the ratio of nitrogen tosilicon is 4:3, but variations in this ratio remain within the scope ofthe definition of silicon nitride as used for the silicon nitride filmsin this disclosure.

A “metal” as used herein and throughout this disclosure refers to, butis not limited to, a material (element, compound, and alloy) that hasgood electrical and thermal conductivity. This may include, but not belimited to, gold, chromium, aluminum, silver, platinum, nickel, copper,rhodium, palladium, tungsten, and combinations of such materials.

An “electrode”, “contact”, “track”, “trace”, or “terminal” as usedherein and throughout this disclosure refers to, but is not limited to,a material having good electrical conductivity and that is typically,optically opaque. This includes structures formed from thin films, thickfilms, and plated films for example of materials including, but notlimited to, metals such as gold, chromium, aluminum, silver, platinum,nickel, copper, rhodium, palladium, tungsten, and combinations of suchmaterials. Other electrode configurations may employ combinations ofmetals, for example, a chromium adhesion layer and a gold electrodelayer.

References to “an embodiment”, “another embodiment”, “yet anotherembodiment”, “one example”, “another example”, “yet another example”,“for example” and so on, indicate that the embodiment(s) or example(s)so described may include a particular feature, structure,characteristic, property, element, or limitation, but that not everyembodiment or example necessarily includes that particular feature,structure, characteristic, property, element or limitation. Furthermore,repeated use of the phrase “in an embodiment” does not necessarily referto the same embodiment.

An embodiment of the inventive dielectric waveguide structure is shownin FIG. 1A-1D. The inventive dielectric waveguide structure is a stackof dielectric films deposited on a substrate 110 to form opticaldielectric interposer 100 (FIG. 1A). In an embodiment, the substrate issilicon. In other embodiments, the substrate is GaAs, InP, SiGe, SiC, oranother semiconductor. In yet other embodiments, the substrate isaluminum nitride, aluminum oxide, silicon dioxide, quartz, glass,sapphire, or another ceramic or dielectric material. In yet otherembodiments, the substrate is a metal. And in yet other embodiments, thesubstrate is a layered structure of one or more of a semiconductor, aceramic, and a metal. It is to be understood that the substrate can beany material that provides a suitable mechanical support. It is to befurther understood that a substrate with an interconnect layer thatcontains electrical lines and traces, separated with intermetaldielectric material, is a substrate.

The optical dielectric interposer 100 includes a planar waveguidestructure formed on substrate 110. In the preferred embodiment, theplanar waveguide structure includes a buffer layer 130, spacer layer138, a repeating stack of silicon oxynitride films 142, a top spacerlayer 150, and an optional top layer 158 (FIG. 1A).

In preferred embodiments, buffer layer 130 is one or more layers ofsilicon dioxide or silicon oxynitride. In some embodiments, the bufferlayer is a layer of silicon oxynitride. In a preferred embodiment, thebuffer layer 130 is a silicon oxynitride layer, 5000 nm in thickness,with an index of refraction of 1.55. In other embodiments, the bufferlayer 130 is silicon oxynitride with refractive index of 1.55 and isthicker than 2000 nm. In other embodiments, the buffer layer 130 is asilicon dioxide layer with a refractive index of approximately 1.445. Inother embodiments, the buffer layer 130 is a silicon dioxide layer witha refractive index of approximately 1.445 that is greater than 2000 nmin thickness. In a preferred embodiment, the buffer layer 130 is asilicon dioxide layer that is approximately 4000 nm in thickness andwith a refractive index of approximately 1.445 (FIG. 1A).

Buffer layer 130 can be a composite layer of one or more layers ofsilicon dioxide or silicon oxynitride with varying thicknesses that insome embodiments sum to greater than 4000 nm in total thickness.Similarly, the buffer layer 130, in some preferred embodiments, can be acomposite layer of one or more layers with varying refractive index,that when combined, provide a total thickness of greater than 4000 nmand a composite refractive index in the range of 1.4 to 2.02 (FIG. 1A).

In preferred embodiments, spacer layer 138 is one or more layers ofsilicon dioxide or silicon oxynitride. In a preferred embodiment, thespacer layer 138 is a single spacer layer 138 a of silicon oxynitride,500 nm in thickness, with an index of refraction of 1.55. In someembodiments, single spacer layer 138 a is a layer of a single material,such as silicon dioxide. In other preferred embodiments, single spacerlayer 138 a is a layer of silicon oxynitride. In yet other preferredembodiments, the single spacer layer 138 a is a layer of siliconoxynitride with refractive index of 1.55 with thickness of 500 nm. Inyet other embodiments, single spacer layer 138 a is a layer of siliconoxynitride with thickness in the range of 0 to 1000 nm. Although inpreferred embodiments, a spacer layer 138 is included in the structure,in some other embodiments, the spacer layer 138, can be combined withthe buffer layer, can be made very thin, or is not included (FIG. 1D).

Spacer layer 138 can be a composite spacer layer 138 b of one or morelayers of silicon oxynitride or silicon dioxide. In an embodiment,composite spacer layer 138 b is includes two layers of siliconoxynitride with thicknesses of 250 nm and with a composite refractiveindex of approximately 1.55. In some embodiments, the sum of thethicknesses of the two layers in composite spacer layer 138 b is in therange of 1 to 1000 nm (FIG. 1D).

Similarly, the spacer layer 138 can be a composite layer 138 c of threeor more layers with the same or varying thicknesses and refractiveindices, that when combined, provide a total thickness in the range of 1nm to 1000 nm and a composite refractive index in the range of 1.4 to2.02 (FIG. 1D).

The combined thicknesses of the buffer layer 130 and the spacer layer138 in embodiments provide spatial separation between the core repeatingstack 142 and the substrate 110 and reduce, minimize, or eliminate theinteraction of the transmitted optical signal with the substrate 110.The transmission of optical signals with low optical loss through therepeating structure 142 requires some degree of confinement of thesignal to the waveguide with minimal interaction of the optical signalswith the substrate 110 in embodiments for which the optical signals areattenuated in the substrate material. Silicon and some othersemiconductors, and metal layers in the interconnect layers, forexample, can lead to significant attenuation of optical signals. Thecombined thicknesses of the buffer layer 130 and the spacer 138 providespatial isolation between the substrate materials and the upper layersof the inventive dielectric stack structure to reduce the interaction oftransmitted optical signals with materials in the substrate that canlead to attenuation (FIG. 1A).

Dielectric stack 142 forms the core of the inventive waveguide structurethrough which optical signals can be transmitted with low optical loss.In preferred embodiments, the dielectric film stack 142 of is a layeredstructure of silicon oxynitride films (FIG. 1A).

In an embodiment, the dielectric stack 142 has a repeating stack 142 aof two dielectric films in which the constituent films within therepeating stack structure 142 a are of differing refractive indices.Differences in the refractive indices can occur primarily from changesin the stoichiometric composition of the films. In preferredembodiments, the changes in the stoichiometry of the films in therepeating film structure 142 is accomplished with changes in the processconditions used in the deposition of the films in the repeating filmstructure 142. In a preferred embodiment, the repeating stack structure142 a includes a first film 143 of 900 nm of silicon oxynitride with anindex of refraction of 1.6 and a second film 144 of 50 nm of siliconoxynitride with an index of refraction of 1.7. In another preferredembodiment, the repeating structure 142 a includes a first film 143 of40 nm of silicon oxynitride with an index of refraction of 1.7 and asecond film 144 of 500 nm of silicon oxynitride with an index ofrefraction of 1.65. In yet another preferred embodiment, the repeatingstructure 142 a includes a first film 143 of 60 nm of silicon oxynitridewith an index of refraction of 1.7 and a second film 144 of 500 nm ofsilicon oxynitride with an index of refraction of 1.65. It is to beunderstood that the order of the first film 143 and the second film 144in embodiments can be reversed and remain within the scope and spirit ofthe invention (FIG. 1C).

In another embodiment, the dielectric stack 142 b has a repeating stack142 of more than two dielectric films in which the constituent films145-147 within the repeating structure 142 a are of differing refractiveindices, and in some embodiments, of the same or differing thicknesses.In an embodiment, repeating stack 142 b includes a first film 145 of 400nm of silicon oxynitride with an index of refraction of 1.6, a secondfilm 146 of 500 nm of silicon oxynitride with an index of refraction of1.65, and a third film 147 of 50 nm of silicon oxynitride with an indexof refraction of 1.7 (FIG. 1C).

In yet other embodiments, the repeating stack 142 c of dielectric stack142 includes more than three layers for which the index of refractionfor the constituent layers of silicon oxynitride is varied to achievethe total film thickness of the overall dielectric stack structure 142.In embodiments, for example, in which the repeating film structure 142 ahas two constituent films with a combined thickness of 600 nm, the stackmust be repeated 15 times to reach an overall thickness of 9 microns forthe dielectric film stack 142. In other embodiments in which the overallthickness of the dielectric film stack is 9 microns, a repeating stackof 45 constituent layers of 100 nm each can be implemented in which theoverall repeating structure 142 a-142 c need only be repeated twice toachieve the overall thickness. In yet other embodiments, the repeatingstructure 142 a-142 c of dielectric stack 142 has a layered filmstructure that does not repeat because the total number of constituentfilms in the repeating stack provides sufficient overall film thicknessfor the film structure 142 (FIG. 1C).

In preferred embodiments, the repeating film structure 142 is acomposite structure of repeating stacks. In embodiments with therepeating stack 142 a, the overall thickness of repeating film structure142 is the combined thickness of the repeating stack 142 a, 142 bmultiplied by the number of times that the repeating stack 142 a-142 bis repeated. For example, the repeating film structure 142 a for apreferred embodiment in which the first layer 143 is 900 nm and thesecond layer 144 is 50 nm has a total repeating stack thickness of 950nm and when repeated 9 times, the resulting combined film thickness fordielectric stack 142 is 8590 nm ((900 nm+50 nm)×9=8590 nm)). Similarly,in another preferred embodiment, the repeating film structure 142 a,which has a first layer 143 that is 40 nm with a refractive index of1.7, and which has a second layer 144 that is 500 nm in thickness with arefractive index of 1.65, has a combined thickness for repeating stack142 of 540 nm, and when repeated 10 times, has a resulting combined filmthickness for dielectric stack 142 of 5400 nm ((500 nm+40 nm)×10=5400nm)) (FIG. 1C).

Generally, the overall dielectric stack 142 is made sufficiently thickto provide the low optical loss for optical signals transmitted throughthe resulting waveguide structure 140. The multilayer structure,deposited at low temperatures, ensures low stress in the resulting filmstructure and enables thick waveguides (2000 nm to 25000 nm) to beformed. Waveguide structures 140 are thus sufficiently thick to enabletransmission of the optical signals with little interaction of thetransmitted optical signals with the substrate, interaction levels thatcould lead to undesired attenuation of the transmitted signals (FIG.1C).

It is to be understood that the thickness, the number of films, and therefractive index for the films in dielectric stack 140 can vary andremain within the scope of the current invention. The refractive indexof silicon oxynitride films can vary in the range of 1.4 to 2.02. As theconcentration of nitrogen in deposited silicon oxynitride films isminimized, the refractive index approaches the index of refraction ofsilicon dioxide, 1.445. Conversely, as the concentration of oxygen isminimized in the deposited films, the refractive index approaches theindex of refraction of silicon nitride, 2.02. The index of refractioncan thusly be varied in the range of 1.445 to 2.02 by varying thestoichiometric concentration of silicon, oxygen, and nitrogen in thedeposited films. In embodiments, the index of refraction for theconstituent films 143, 144 in the repeating dielectric film stack 142 a,for example, are varied in the range of 1.445 to 2.02 to produce thickfilm structures of 2000 to 25000 nm, or greater, and that provide lowstress and low optical signal losses, in dielectric film stacks 140(FIG. 1C).

In another preferred embodiment, the dielectric film stack 142 includesa repeating stack 142 a with a first layer 143 of silicon oxynitridewith thickness of 60 nm and an index of refraction of 1.7 and a secondlayer 144 of silicon oxynitride with thickness of 500 nm and an index ofrefraction of 1.65. Repeating dielectric stack structure 142 a isrepeated in an embodiment 13 times for a total thickness for dielectricfilm stack 142 of 7280 nm. It is to be understood that the total numberof repeating film stacks 142 a can vary. In some preferred embodiments,the number of repeating film stacks 142 a is three to twenty. In someother preferred embodiments, the repeating film stack 142 a is such toproduce a total dielectric film structure 142 that in some embodimentsis greater than 2000 nm in thickness and in some embodiments less than25000 nm. In yet other preferred embodiments, the total dielectric filmstructure 142 is in the range of 8000 to 12000 nm. In yet otherembodiments, the number of repeating film stacks 141 is two or more andthe thickness of the dielectric film structure 142 is greater than 2000nm and less than 25000 nm (FIG. 1C).

In some embodiments, the thickness for the first film 143 is in therange of 5 nm to 1000 nm. In some other embodiments, the thickness ofthe second film 144 is in the range of 5 nm to 1000 nm. In these andother embodiments, the thickness of the dielectric film structure 142,which is the sum of the thicknesses of the repeating film structures 142a, is greater than 2000 nm in thickness. In preferred embodiments, thethickness of the sum of the repeating film structures 142 a is in therange of 4000 to 10000 nm (FIG. 1C).

It is to be understood that the repeating film structure 142 a is anintegral component of the inventive dielectric stack structure 140. Itis also to be understood that the number of films, the film thicknesses,the refractive indices, and the resulting composition of the films canbe varied and remain within the spirit and scope of the inventivedielectric stack structure 140, and in the practice of utilizing thedielectric stack structure 140 to provide low stress and low opticalloss for signals transmitted through waveguides that are fabricated fromthe dielectric stack structure 140. In this regard, in some embodiments,an initial repeating film structure 142 a is used for two or more of thefilms in the dielectric stack 142, and then a different repeating filmstructure 142 a is used for another two or more films in the samedielectric film structure 140 to produce inventive dielectric stack 140.It is to be further understood that an initial repeating film structure142 a can be used for two or more of the films in the dielectric filmstructure 142, a different repeating film structure 142 a, can be usedfor another two or more films in the same dielectric film structure 142,and then any number of additional repeating film structures 142 a withthe same or different repeating film structures can be used for two ormore additional films in the dielectric film structure 140 and remainwithin the scope and spirit of the embodiments. In the foregoingdiscussion, the variations in the first film 143 and second film 144 canbe produced with one or more variations in the refractive index, thethickness, and the composition or stoichiometry of the films (FIG. 1C).

It is also to be understood that in some embodiments, first film 143 inthe repeating film structure 142 a can include one or more films andremain within the scope of the invention. In an embodiment, first film143 in repeating film structure 142 a, for example, is 500 nm inthickness with a refractive index of 1.7. In another embodiment, firstfilm 143 includes a first part that is 250 nm in thickness with arefractive index of 1.7 and a second part that is 250 nm in thicknesswith a refractive index of 1.65. In yet another embodiment, the firstfilm 143 in the repeating film structure 142 a has a refractive index of1.68 with a first partial thickness that is 250 nm and a second partialthickness that is deposited in a separate process step from the first,for example, and that is also 250 nm in thickness for a combinedthickness of 500 nm for the two partial films of the first film 143 ofrepeating film structure 142 a (FIG. 1C).

In some embodiments, the first film 143 has a graded refractive index orstoichiometric composition. Gradations in the composition of the firstfilm 143 of the repeating film structure 142 a, for example, remainwithin the scope of the current invention. In some embodiments, therefractive index varies through part or all of the thickness of thefirst film 143. Similarly, in some embodiments, the stoichiometriccomposition varies through part or all of the thickness of the firstfilm 143. Variations in the refractive index or the stoichiometriccomposition of the first film 143 within the thickness of this filmremain within the scope of the current invention (FIG. 1C).

It is also to be understood that in some embodiments, second film 144 inthe repeating film structure 142 a can include one or more films andremain within the scope of the invention. In an embodiment, second film144 in repeating film structure 142 a, for example, is 500 nm inthickness with a refractive index of 1.7. In another embodiment, secondfilm 144 includes a first part that is 250 nm in thickness with arefractive index of 1.7 and a second part that is 250 nm in thicknesswith a refractive index of 1.65. In yet another embodiment, the secondfilm 144 in the repeating film structure 142 a has a refractive index of1.68 with a first partial thickness that is 250 nm and a second partialthickness that is deposited in a separate process step from the first,for example, that is also 250 nm for a combined thickness of 500 nm forthe two partial films of the second film 144 of the repeating filmstructure 142 a (FIG. 1C).

In some embodiments, the second film 144 has a graded refractive indexor stoichiometric composition. Gradations in the composition of thesecond film 144 of the repeating film structure 142 a, for example,remain within the scope of the current invention. In some embodiments,the refractive index varies through part or all of the thickness of thesecond film 144. Similarly, the stoichiometric composition variesthrough part or all of the thickness of the second film 144. Variationsin the refractive index or the stoichiometric composition of the secondfilm 144 within the thickness of this film remain within the scope ofthe current invention.

In some embodiments, repeating structure 142 has an unequal number offirst layers 143 and second layers 144. In some embodiments, repeatingstructure 142 includes a first layer 143 positioned between two secondlayers 144 (FIG. 1C).

In preferred embodiments, top spacer layer 150 is one or more layers ofsilicon dioxide or silicon oxynitride. In some embodiments, singlespacer layer 150 a is a layer of one type of material, such as silicondioxide. In some preferred embodiments, single spacer layer 150 a is alayer of silicon oxynitride. In yet other preferred embodiments, thesingle spacer layer 150 a is a layer of silicon oxynitride withrefractive index of 1.55 and with a thickness of 500 nm. In yet otherembodiments, single spacer layer 150 a is a layer of silicon oxynitridewith thickness in the range of 0 to 1000 nm. Although in preferredembodiments, a spacer layer 150 a is included in the structure, in someother embodiments, the spacer layer 150 can be combined with an optionaltop layer, can be made very thin, or is not included (FIG. 1B).

Spacer layer 150 can be a composite spacer layer 150 b of one or morelayers of silicon oxynitride or silicon dioxide. In an embodiment,composite spacer layer 150 b includes two layers of silicon oxynitridewith thicknesses of 250 nm and with a composite refractive index ofapproximately 1.55. In some embodiments, the sum of the thicknesses ofthe two layers in composite spacer layer 150 b is in the range of 1 to1000 nm (FIG. 1B).

Similarly, the spacer layer 150 can be a composite layer 150 c of threeor more layers with the same or different thicknesses and refractiveindices, that when combined, provide a total thickness in the range of 1nm to 1000 nm and a composite refractive index in the range of 1.4 to2.02 (FIG. 1B).

Optional top layer 158 is one or more layers of a dielectric materialsuch as silicon dioxide, silicon nitride, aluminum oxide, and aluminumnitride, among others. In some embodiments, a top layer 158 of silicondioxide with thickness of 200 nm and a refractive index of 1.445 isused. In some embodiments, the film thickness of the top layer is in therange of 0 to 500 nm. In some embodiments, silicon oxynitride is used inthe optional top layer 158. In some embodiments, another dielectricmaterial or combination of materials such as aluminum nitride oraluminum oxide is used. In some embodiments, no optional top layer 158is provided (FIG. 1A).

The advantages of the current invention with regard to achievable rangesof the measured film stress for films that can be implements infabricating dielectric film structures are shown in FIG. 2A-2B for someembodiments. In FIG. 2A, the measured film stress is shown for a rangeof thicknesses for the inventive dielectric film stacks. FIG. 2A showsthat the film stress can be controlled to less than approximately 20 MPafor embodiments as thick as approximately 18 um. These relatively lowstress levels are not achievable or very difficult to achieve in filmsof a single thick layer of material such as silicon dioxide or siliconoxynitride. In FIG. 2B, the measured stress levels for deposited siliconoxynitride films are shown for films of various refractive indices. Asshown, the refractive index is a convenient means for assessingvariations in film properties for deposited films. The capability toachieve control of the stress in the individual films over a wide range,allows for the fabrication of very thick dielectric film structures(1000-25000 nm, and greater) with optical properties that are suitablefor use as planar waveguides. In embodiments, stress levels arecontrolled in planar waveguide structures to minimize deformation of thesubstrates upon which the thick dielectric stacks are deposited, and toachieve low optical signal loss in waveguides fabricated from thesethick dielectric film structures.

Referring to FIG. 3A-3B, the measured optical losses from someembodiments of the inventive dielectric stack structures are shown.Optical signal losses for practical use in planar waveguide structuresof less than approximately 1 dB/cm are desirable. FIG. 3A shows thatthese levels are achievable for a range of measured composite refractiveindices from the inventive dielectric stack structures. In addition tothe properties of the dielectric stack structure itself, the bufferlayer also has an influence on the measured losses for optical signalstransmitted through waveguides fabricated from the inventive dielectricstack structures. FIG. 3B shows how the thickness of the buffer layer insome embodiments affects the measured optical losses. As the thicknessof the buffer layer is increased in these embodiments, the resultingoptical losses are reduced to values of much less than 1 dB/cm.

Referring to FIG. 4A-4C, steps in the formation of embodiments of thedielectric films and film structures are provided. In FIG. 4A, formingstep 400 in the process of forming embodiments of the inventivedielectric stack 140 of silicon oxynitride films at low temperaturehaving low stress and low optical loss is shown. Low temperature in FIG.4A refers to the temperature of the deposition of the films used in thefabrication of the dielectric stacks, namely less than 400 C in someembodiments, and in preferred embodiments, less than or equal to 300 C.Low stress in FIG. 4A refers to stress levels in the deposited films infilm structure 140 of less than or equal to approximately 20 MPa, eithercompressive or tensile. Low optical loss in FIG. 4A refers to opticallosses in embodiments of deposited dielectric film stacks 140 of lessthan approximately 1 dB/cm. The forming step 400 provides for theformation of thick structures of dielectric silicon oxynitride filmswith low stress, and suitable for use in the transmission of opticalsignals with low loss.

Referring to FIG. 4B, the forming steps 420 in embodiments for whicheach individual layer in the inventive dielectric stack 140 of siliconoxynitride films is deposited at low temperature, and with low stressand low optical loss is shown. Low temperature in FIG. 4B refers to thetemperature of the deposition of the films used in the fabrication ofthe dielectric stacks, namely less than 400 C in some embodiments, andin preferred embodiments, less than or equal to 300 C. Low stress inFIG. 4B refers to stress levels in the deposited films of less than orequal to approximately 20 MPa, either compressive or tensile. Stresslevels of less than 20 MPa in deposited films ensure minimal substratedeformation and reduce the likelihood that the films will delaminate.Low optical loss in FIG. 4B refers to optical losses in embodiments ofdeposited dielectric film stacks 140 of less than approximately 1 dB/cm.Forming step 420 provides for the formation of thin composite films ofdielectric silicon oxynitride deposited sequentially at low temperaturesof less than 400 C to form the thick dielectric stack structures 140with low stress, and suitable for use in the transmission of opticalsignals with low loss.

Referring to FIG. 4C, steps in the formation of planar waveguides from aforming step 440 and a patterning step 450 are shown for someembodiments. Formation of the individual dielectric films and thedielectric film structures 440 for the inventive stack structure 140 areshown that include the formation of a dielectric stack of siliconoxynitride films on a substrate 110 with a stack structure that includesa buffer layer 130, one or more optional bottom spacer layers 138, arepeating stack of one or more dielectric layers 142, one or moreoptional top spacer layers 150, and an optional top layer 158.Embodiments for the forming of the dielectric film and film structures440 utilize one or more of forming step 400 and forming step 420.Patterning step 450 is combined in embodiments with forming step 440 onthe resulting dielectric stack to form one or more planar waveguidesfrom the dielectric stack structures 140. Patterning steps can includethe use of established photoresist patterning processes, in whichphotosensitive layers are used either directly as a means fortransferring a pattern with subsequent dry or wet etch processing, orvia a hard mask in which the photoresist is first used to transfer apattern to a hard mask layer that is then used to transfer the waveguidepattern from the hard mask layer to the dielectric stack layer.Processes for photoresist patterning and subsequent wet and dry etchingof film structures are well established for those skilled in the art ofdielectric film patterning techniques.

Referring to FIG. 5A, a cross sectional schematic of an embodiment ofthe inventive optical dielectric interposer structure 500 is shown. Inthis figure, an embodiment for interposer 500 includes substrate 510,optional interconnect layer 520, and planar dielectric stack structure540 disposed on the optional interconnect layer 520. Terminal padopening 525 in the interconnect layer 520 provides for connections ofoptical die to the interconnect metal lines. In some embodiments, thetop intermetal dielectric 527 in the interconnect layer resides belowthe dielectric stack 540 as shown in FIG. 5A. The interconnect layer 520is a structure of metal lines 526 and intermetal dielectric films 527that provide metal traces for mounting optical devices and forinterconnecting electrical and optoelectrical die on the dielectricinterposer 500. In some embodiments, the top layer of the interconnectlayer 520 may be electrically conductive or insulating, or may beelectrically conducting in some areas and insulating in some areas. Inpreferred embodiments in which optical, electrical, or optoelectricaldie are mounted onto the interposer 500, metal traces are routed withinthe interconnect layer 520 that are accessible through openings 525 toprovide electrical and mechanical connections for the optical,electrical, and optoelectrical devices in, on, or connected to theinterposer 500. It is to be understood that the mounting of purelyoptical die (i.e., die that have an optical function but that are notelectrical) as in a discrete waveguide for example, can benefit from themethods of mechanical attachment commonly used in the attachment ofelectrical die. Attachment of purely optical devices using electricalbond pads is within the scope of the current invention as describedherein. It is also important to note that the top layer of theintermetal dielectric 527 can provide the same functionality as thebuffer layer 530 in some embodiments as shown in FIG. 5A.

The inclusion of optical, electrical, and/or optoelectrical devices,forms a sub mount assembly 505 from the inventive optical dielectricinterposer 500. FIG. 5B shows a cross sectional schematic of anembodiment of a sub mount assembly 505 with an optical fiber 590positioned to provide an optical pathway for the transmission of opticalsignals between the optical fiber 590 and the planar dielectric stack540. FIG. 5B also shows optical, electrical, or optoelectrical device560 and electrical device 562 mounted to terminal pad openings 525 ininterconnect layer 520. In an embodiment, optical signals are receivedfrom optical fiber 590 into a waveguide fabricated from the planardielectric stack 540 and routed to device 560 for processing,re-routing, or conversion to electrical signals, for example.

In other embodiments, the optical signals originate on the sub mountassembly 505 and are transmitted through waveguides fabricated fromplanar dielectric stack structure 540 to the optical fiber 590. In yetother embodiments, the signals are both received from, and transmittedto, the optical fiber 590.

Referring to FIG. 6A-6B, cross sectional schematics of embodiments ofthe inventive optical dielectric interposer structure 600 and the submount assembly 605 are shown. In FIG. 6A, an embodiment for interposer600 includes substrate 610, optional interconnect layer 620, and planardielectric stack structure 640 disposed on the optional interconnectlayer 620. Interconnect layer 620 is typically provided in embodimentsfor which interconnects are required for optical or electrical diemounted on the interposer 600 to form a submount assembly. Terminal padopening 625 in the interconnect layer 620 provides connections for theoptical and electrical die to the interconnect metal lines 626.Interconnect metal lines 626 within interconnect layer 620 forminterconnects between electrical devices mounted onto the interposer600, and in some embodiments, to form electrical connections for devicesexternal to the interposer 600. In embodiments, the planar dielectricstack 640 includes buffer layer 630. In some other embodiments, openingsin the buffer layer 630 provide access to underlying metal layers 626through the interconnect layer openings 625. It is to be understood thatthe buffer layer 630 can be utilized for multiple purposes on theinterposer 600 that include isolation, insulation, vertical spacing,alignment, and control of optical loss. In some embodiments, thepatterning of the buffer layer 630 is not coincident with the pattern ofthe other layers in waveguides that are fabricated from the inventivedielectric stack structure 640. In yet other embodiments, the bufferlayer can be a part of the intermetal dielectric 627 of the interconnectlayer 620.

In embodiments, the intermetal dielectric 627 in the interconnect layer620 generally provides electrical isolation for the metal interconnects626. The interconnect layer 620 is a structure of metal lines 626 andintermetal dielectric 627 that provide insulated electricalinterconnections for the electrical and optoelectrical die on thedielectric interposer 600, and in some embodiments, allow for theinterconnection of devices mounted external to the interposer 600 butfor which connections are required within the interposer 600. It isunderstood that optical devices that do not require electricalinterconnection can also be attached in some embodiments to interconnectlayers for the purpose of mechanical attachment without a specificrequirement for electrical interconnection.

The inclusion of electrical, optical, and/or optoelectric devices formsa sub mount assembly 605 from the optical interposer 600 on substrate610 with interconnect layer 620. In FIG. 6B, a cross sectional schematicof an embodiment of a sub mount assembly 605 with an optical fiber 690positioned to provide an optical pathway between the optical fiber 690and planar dielectric stack 640 is shown. FIG. 6B also showsoptoelectrical device 660 and electrical device 662 mounted throughbuffer layer 630 to terminal pad openings 625 and connected to metalinterconnect lines 626 in interconnect layer 620. In embodiments,intermetal dielectric 627 provides electrical insulation for the metalinterconnects 626. In an embodiment, optical signals are received fromoptical fiber 690, are directed into planar waveguides fabricated frominventive dielectric stack 640, and routed to aligned optical oroptoelectrical device 660 for processing, re-routing, or conversion toelectrical signals, for example.

Referring to FIG. 7A-7B, cross sectional schematics of embodiments ofthe inventive optical dielectric interposer 700 and sub mount assembly705 are shown. In FIG. 7A, an embodiment for interposer 700 includessubstrate 710, interconnect layer 720, inventive planar dielectric stackstructure 740 disposed on interconnect layer 720, and integratedelectrical device 764. In some embodiments, integrated electrical device764 in the underlying substrate 710 is a transistor, capacitor,resistor, inductor, or other electrical device. In other embodiments,integrated electrical device 764 is a p-channel metal oxidesemiconductor (PMOS) transistor, an n-channel metal oxide semiconductor(NMOS) transistor device or array of one or more of these devices. Insome embodiments, the electrical device 764 is an array of transistordevices based on complementary metal oxide semiconductor (CMOS)technology. In some embodiments, transistor arrays 764 in the substrate710, are used for signal processing, signal conditioning, signalgeneration, memory, and computation, for example. In some embodiments,terminal pad openings 725 in the interconnect layer 720 provideelectrical connections between optoelectrical die and the interconnectmetal lines 726. In some embodiments, the top intermetal dielectric 727in the interconnect layer 720 resides below the dielectric stack 740 asshown in FIG. 7A, and in some embodiments, the upper layer of theintermetal dielectric 727 can also serve as the buffer layer 730. Theinterconnect layer 720 is a structure of metal lines 726 and intermetaldielectric 727 that provide electrical connections for interconnectingelectrical and optoelectrical devices and die that are fabricated on,mounted in, or are connected external to the dielectric interposer 700.

In some embodiments, the top layer of the interconnect layer 720 may beelectrically conductive or insulating. Some parts of the top layer ofinterconnect layer 720 can be insulating, and some parts of the toplayer of interconnect layer 720 can be conductive. In preferredembodiments in which electrical or optoelectrical die are mounted ontothe interposer 700, metal lines 726 are routed within the interconnectlayer 720 to provide electrical connections for the devices in, on, orconnected to the interposer 700, and to underlying electrical devices764.

Submount assembly 705 is formed from the optical dielectric interposer700 by the inclusion of optical, electrical, and optoelectric devices760 onto the interposer 700. FIG. 7B shows a cross sectional schematicof an embodiment of a sub mount assembly 705 with optical fiber 790positioned to provide an optical pathway between the optical fiber 790and a waveguide fabricated from the inventive planar dielectric stack740. FIG. 7B also shows optoelectrical device 760 mounted to terminalpad openings 725 on interconnect layer 720. In embodiments, opticalsignals are received from optical fiber 790, into planar waveguidesformed from the inventive dielectric stack 740 and routed tooptoelectrical or optical device 760 for processing, re-routing, orconversion to electrical signals, for example. In some embodiments,optoelectrical die 760 are connected to one or more of electricaldevices 764 via metal lines 726 in the interconnect layer 720. In theseembodiments, the optical signals may also originate, wholly or in part,on the sub mount assembly 705 from which the signals can be transmittedthrough the planar waveguide structures 740 to the optical fiber 790.

In other embodiments, the optical signals originate on the sub mountassembly 705 and are transmitted through one or more planar waveguidestructures formed from the inventive dielectric stack 740 to the opticalfiber 790. In yet other embodiments, the signals are received from theoptical fiber 790 for one or more of processing, routing, and conversionto electrical signals.

Referring to FIG. 8A-8B, cross sectional schematics of embodiments ofthe inventive optical dielectric interposer 800 and sub mount assembly805 are shown. In FIG. 8A, an embodiment for interposer 800 includessubstrate 810, optional interconnect layer 820, inventive planardielectric stack structure 840 disposed on the optional interconnectlayer 820, and integrated electrical device 864 in substrate 810

In some embodiments, integrated electrical device 864 in the underlyingsubstrate 810 is a transistor, capacitor, resistor, inductor, or otherelectrical device. In other embodiments, integrated electrical device864 is a p-channel metal oxide semiconductor (PMOS) or n-channel metaloxide semiconductor (NMOS) device, or array of one or more of thesedevices. In other embodiments, electrical device 864 is an array oftransistors based on complementary metal oxide semiconductor (CMOS)technology. In some embodiments, transistor arrays 864 in the substrate810 are used for signal processing, signal conditioning, signalgeneration, memory, and computation, for example. In some embodiments,the terminal pad opening 825 in the interconnect layer 820 provides forelectrical connections of optoelectrical die to the interconnect metallines 826 in interconnect layer 820. In some embodiments, the top layerof the intermetal dielectric 826 in the interconnect layer 820 residesbelow the dielectric stack 840. In some embodiments, the planardielectric stack 840 includes buffer layer 830. In yet other embodimentswith buffer layer 830 in dielectric stack 840, the buffer layer 830resides within or above the interconnect layer 820. Interconnect layer820 is typically provided in embodiments for which interconnects arerequired for optoelectrical die mounted on the interposer 800 to form asub mount assembly 805. The interconnect layer 820 is a structure ofmetal lines 826 and intermetal dielectric films 827 that provide metalconnections for interconnecting optical, electrical, and optoelectricaldevices and dies that are fabricated on, mounted in, or connectedexternal to the dielectric interposer 800.

In some embodiments, the terminal pad openings 825 in the interconnectlayer 820 provide connections for optoelectrical die 860 to theinterconnect metal lines 826 as shown in FIG. 8B. Interconnect metallines 826 within interconnect layer 820 form interconnects betweenoptoelectrical devices 860 and optional electrical devices (not shown)mounted onto the interposer, or to form connections for one or more ofoptoelectrical devices and electrical devices connected external to theinterposer 800.

In some embodiments, the top layer of the interconnect layer 820 may beelectrically conductive or insulating. In preferred embodiments in whichoptical die are to be mounted onto the interposer 800, metal traces 826are routed within the interconnect layer 820 that are accessible throughopenings 825 to provide electrical and mechanical connections for theoptical, electrical, and optoelectrical devices in, on, or connected tothe interposer 800, and to the underlying electrical device 864. It isto be understood that the mounting of purely optical die (i.e, die thathave an optical function but that are not electrical) as in a discretewaveguide for example, can benefit from the methods of mechanicalattachment commonly used in the attachment of electrical die. Attachmentof purely optical devices using electrical bond pads is within the scopeof the current invention as described herein.

In some embodiments, intermetal dielectric 827 in the interconnect layer820 provides electrical isolation for the metal interconnects 826. Theinterconnect layer 820 is a structure of metal traces 826 and intermetaldielectric 827 that provides electrically insulated interconnections forthe optical, electrical, and optoelectrical die 860 on the dielectricinterposer 800, and in some embodiments, allow for the interconnectionof devices mounted external to the interposer 800 but for whichconnections are required within the interposer 800.

Submount assembly 805 is formed from the optical interposer 800 by theinclusion of electrical, optical, optoelectric devices 860 onto theinterposer 800. FIG. 8B shows a cross sectional schematic of anembodiment of a sub mount assembly 805 with optical fiber 890 positionedto provide an optical pathway between the optical fiber 890 and awaveguide fabricated from the inventive planar dielectric stack 840.FIG. 8B also shows optoelectrical device 860 mounted to terminal padopenings 825 in interconnect layer 820. In some embodiments, terminalpad openings 825 are provided through openings in the buffer layer 830,or another layer on the surface of the interconnect layer 820. In someembodiments, optical signals are received from optical fiber 890, intoplanar waveguides formed from the inventive dielectric stack 840 androuted to optoelectrical or optical device 860 for processing,re-routing, or conversion to electrical signals, for example. In someembodiments, optoelectrical die 860 are connected to one or moreelectrical devices 864 via metal lines 826 in the interconnect layer820.

In other embodiments, the optical signals originate on the sub mountassembly 805 and are transmitted through planar waveguides formed fromthe inventive dielectric film structure 840 to the optical fiber 890. Inyet other embodiments, the signals are received from the optical fiber890 to the sub mount assembly 805 for one or more of processing,routing, and conversion to electrical signals.

Referring to FIG. 9A-9D, cross sectional schematics of embodiments ofthe inventive optical dielectric interposer structure 900 and sub mountassembly 905 are shown. In FIG. 9A, interposer 900 is shown and includessubstrate 910 and interconnect layer 920. Interconnect layer 920 is astructure of metal traces 926 and intermetal dielectric material 927within which conductive pathways are provided for interconnectingelectrical and optoelectrical devices and die that are formed on,mounted in, or connected to the dielectric interposer 900. In someembodiments, interconnected devices are interconnected to the interposer900 from an external mount or sub mount assembly. The dotted lines ininterconnect layer 920 shown in FIG. 9A schematically represent examplesof electrical pathways 926 within the interconnect layer 920 forinterconnecting optoelectrical devices and electrical devices mounted toterminal pad interconnect openings 925, for example. FIG. 9A showsinventive dielectric stack 940 mounted via bonding pads 922 as adiscrete dielectric waveguide component 965 to interconnect layer 920.In some embodiments, the dielectric stack 940 is fabricated or formedindependently of the substrate 910 and the interconnect layer 920, andthen added as a discrete element to form interposer 900. It is importantto note that the formation of interposer 900 may be accomplishedconcurrently with the formation of sub mount assembly 905 forembodiments in which the discrete waveguide components 965, withinventive dielectric stack 940, are added to interposer 900 concurrentlywith optoelectrical and electrical components 960 as shown in FIG. 9B.

In embodiments, discrete waveguide component 965, fabricated with theinventive dielectric stack 940, is a simple conduit for the transmissionof optical signals. In other embodiments, one or more discrete waveguidecomponents 965 on sub mount assembly 905 are conduits for thetransmission of optical signals from an optical fiber attached to thesub mount assembly to one or more locations on the sub mount assembly.In yet other embodiments, discrete waveguide components 965 on sub mountassembly 905 are conduits for the transmission and distribution ofoptical signals from one or more optical fibers attached to the submount assembly to one or more locations on the sub mount assembly 905.In yet other embodiments, discrete waveguide components 965 on sub mountassembly 905 can include one or more of a spot size converter, a filter,an arrayed waveguide, a multiplexers, a demultiplexer, a grating, apower combiner, and the like.

In FIG. 9B, inventive planar dielectric stack structure 940 is shown asdiscrete waveguide component 945 attached to the interconnect layer 920on substrate 910. Submount assembly 905 is formed from the opticaldielectric interposer 900 by the inclusion of optical, electrical, andoptoelectrical devices 960, 962 onto the interposer 900. FIG. 9B shows across sectional schematic of an embodiment of a sub mount assembly 905with optical fiber 990 positioned to provide an optical pathway to thediscrete dielectric waveguide component 965. In the embodiment shown inFIG. 9B, the inventive planar dielectric stack 940 is a pre-fabricateddiscrete optical waveguide component 965 mounted to interposer 900. FIG.9B shows optoelectrical device 960 mounted to terminal pad openings 925in interconnect layer 920 to form sub mount assembly 905. In anembodiment, optical fiber 990 is aligned to discrete waveguide 965,formed from inventive dielectric stack 940, which is further aligned tooptical device 960 to allow for the receiving and sending of opticalsignals for processing, re-routing, or conversion to electrical signals,for example. Optical alignment of devices to the waveguide, inembodiments, provides less than 1 dB power loss, and in preferredembodiments, less than 0.5 dB. Accurate alignment is essential toreducing power loss to tolerable levels.

Terminal pad openings 925 in the interconnect layer 920 provide forconnections of optoelectrical die 960 to the interconnect metal traces926. In preferred embodiments in which optoelectrical die 960 aremounted onto the interposer 900, metal traces 926 are routed within theinterconnect layer 920 to provide electrical and mechanical connections926 for optical, electrical, and optoelectrical devices in, on, orconnected to the interposer 900. In embodiments, the intermetaldielectric 927 in the interconnect layer 920 provides electricalisolation for the metal interconnects 926. The interconnect layer 920 isa structure of metal lines and traces 926 and intermetal dielectric 927that provide interconnections for the optical, electrical, andoptoelectrical die 960, 962 on the dielectric interposer 900, and insome embodiments, allow for the interconnection of devices mountedexternal to the interposer 900 but for which connections are required onor within the interposer 900.

In FIG. 9C, interposer 900 is shown and includes substrate 910,interconnect layer 920, discrete waveguide component 965, and integratedelectrical device 964. Interconnect layer 920 is a structure of metallines and traces 926 and intermetal dielectric material 927 within whichconductive pathways for interconnecting electrical and optoelectricaldevices 960, 962 that are fabricated on, mounted in, or connected froman external sub mount assembly to the dielectric interposer 900, orprovided in underlying substrate 910. The dotted lines in interconnectlayer 920 shown in FIG. 9C schematically represent examples ofelectrical pathways 926 within the interconnect layer 920 forinterconnecting optoelectrical devices 960 and electrical devices 962mounted to terminal pad interconnect openings 925. In preferredembodiments in which optoelectrical die 960 are mounted onto theinterposer 900, metal interconnects 926 are routed within theinterconnect layer 920 to provide electrical and mechanical connectionsfor electrical and optoelectrical devices in, on, or connected to theinterposer 900, and to the underlying electrical devices 964. Integratedelectrical device 964 in underlying substrate 910, in some embodiments,is one or more of a transistor, capacitor, resistor, inductor, or otherelectrical device, or array of electrical devices. In other embodiments,integrated electrical device 964 is ap-channel metal oxide semiconductor(PMOS) transistor or an n-channel metal oxide semiconductor (NMOS)device, or array of one or more of these devices. In yet otherembodiments, device 964 is an array of transistors based oncomplementary metal oxide semiconductor (CMOS) transistor technology. Inyet other embodiments, the integrated electrical device 964 is a bipolartransistor or an array of bipolar transistor devices. In yet otherembodiments, the integrated electrical device 964 is a field effecttransistor or an array of field effect transistors. In some embodiments,transistor arrays 964 in the substrate 910, are used for signalprocessing, signal conditioning, signal generation, memory, andcomputation, for example.

In FIG. 9C, the inventive dielectric stack 940 is shown in the form of adiscrete dielectric waveguide component 965 mounted to interconnectlayer 920 via bonding pads 922. In some embodiments, the dielectricstack 940 is fabricated independently of the substrate 910 and theinterconnect layer 920, and then added as a discrete element to forminterposer 900 as shown, for example, in FIG. 9C. Although electricalconnections are not required for optical waveguides, bonding pads 922,in some embodiments, are similar to bond pads used to form electricalconnections. In other embodiments, other adhesion methods are used thatinclude adhesive, epoxy, or other bonding material.

Submount assembly 905, shown in FIG. 9D, is formed from the opticalinterposer 900 with the inclusion of electrical, optical, optoelectricdevices on the interposer 900. It is important to note that theformation of inventive interposer 900 with the addition of the discretewaveguide 965 is accomplished concurrently with the formation of submount assembly 905 for embodiments in which the discrete waveguidecomponents 965 are added to interposer 900 concurrently with optical,optoelectrical, and electrical components 960. FIG. 9D shows a crosssectional schematic of an embodiment of a sub mount assembly 905 withoptical fiber 990 positioned to provide an optical pathway between theoptical fiber 990 and a planar waveguide 965 fabricated from theinventive planar dielectric stack 940. FIG. 9D also shows optoelectricaldevice 960 mounted to terminal pad openings 925 in interconnect layer920. In an embodiment, optical signals are received from optical fiber990, into planar waveguides 965 formed from the inventive dielectricstack 940 and routed to optoelectrical or optical device 960 forprocessing, re-routing, or conversion to electrical signals, forexample. In some embodiments, optoelectrical die 960 are connected toone or more electrical devices 962 and integrated electrical devices 964via metal lines 926 in the interconnect layer 920. In embodiments,optical fiber 990 is aligned to discrete waveguide 965, formed frominventive dielectric stack 940, which is further aligned to opticaldevice 960 to allow for the receiving and sending of optical signals forprocessing, re-routing, or conversion to electrical signals, forexample. Optical alignment of devices to the waveguide, in embodiments,provides less than 1 dB power loss and in other embodiments, less than0.5 dB. In preferred embodiments, power loss is much less than 0.5 dB.Accurate alignment between the optical fiber and the discrete waveguide965 fabricated from the inventive dielectric stack 940, and between thedielectric stack 940 and the optical or optoelectrical device 960, isnecessary to reduce potential power loss to tolerable levels.

In some embodiments, the optical signals originate on the sub mountassembly 905 and are transmitted through planar dielectric waveguidestructure 940 to the optical fiber 990. In yet other embodiments, thesignals are received from the optical fiber 990 for one or more ofprocessing, routing, and conversion to electrical signals.

Referring to FIG. 10A, the steps of forming a dielectric interposer witha patterned waveguide from the inventive dielectric stack structure areshown that include a providing step 1000, a depositing step 1010, and apatterning step 1020.

In providing step 1000, a substrate is provided with one or moreoptoelectrical or electrical devices coupled to an interconnectionlayer. In embodiments, these devices are one or more of a transistor,capacitor, resistor, inductor, or other electrical device, or an arrayof one or more electrical devices. In other embodiments, these devicesare one or more of a p-channel metal oxide semiconductor (PMOS)transistor and an n-channel metal oxide semiconductor (NMOS) device ordevices. In yet other embodiments, the devices are an array oftransistors based on complementary metal oxide semiconductor (CMOS)transistors technology. In yet other embodiments, the one or moredevices coupled to the interconnection layer as described in providingstep 1000 in FIG. 10A is a bipolar transistor, two or more bipolartransistors, or an array of bipolar transistor devices. In yet otherembodiments, the one or more devices is a field effect transistor, twoor more field effect transistors, or an array of field effecttransistors. In some embodiments, transistor arrays coupled to theinterconnect layer are used for signal processing, signal conditioning,signal generation, memory, and computation, for example.

In depositing step 1010, a stack of dielectric layers is deposited onthe substrate to form the unpatterned inventive dielectric stack on thesubstrate, which is then patterned in patterning step 1020 to form theinventive interposer. In some embodiments, the patterned dielectricstack structure can be a section of waveguide aligned to an optical orelectrical device, for example, for the transmission of optical signalsto and from an optical fiber connected to the sub mount assembly. Inother embodiments, these waveguides can include sections of theinventive dielectric stack that are patterned spot size converters,filters, arrayed waveguides, multiplexers, demultiplexers, gratings,power combiners, and the like. In yet other embodiments, thesewaveguides can provide part of a mechanical structure for the formationof hermetic seals. In yet other embodiments, theses waveguides can be acombination of one or more of these types of structures fabricated fromthe inventive dielectric stack structure. In yet other embodiments, thebuffer layer and the layers of the repeated stack are patterned to forma filter, an arrayed waveguide, a grating, a multiplexer, ademultiplexer, a spot size converter, or a power combiner, and the like.

In embodiments, the patterning step 1020 is used to pattern the blanketdielectric stack structures into one or more planar waveguides.Patterning steps can include the use of established photoresist layers,used either directly as a mask for wet or dry etching or etchprocessing, or via a photoresist layer used to transfer a pattern fromthe photoresist to a hard mask which is utilized for wet or dry etchingor etch patterning of the inventive dielectric film stack. Processes forphotoresist patterning and subsequent wet and dry etching of filmstructures are well established for those skilled in the art ofdielectric film patterning techniques.

Referring to FIG. 10B, steps of forming a sub mount assembly with theinventive interposer are shown that include providing step 1040, a firstcoupling step 1050, and a second coupling step 1060. In providing step1040, a substrate is provided wherein the substrate includes at least afirst device coupled to an interconnection layer, wherein the substrateincludes a waveguide patterned from a stack of dielectric layers.Patterned waveguide structures include filters, arrayed waveguides,gratings, multiplexers, demultiplexers, spot size converters, powercombiners, and the like. In the first coupling step 1050, a seconddevice is coupled to the substrate, wherein the device is configured tointerface between the waveguide and the at least a device. Inembodiments, the second device is a receiving device, for example, suchas a photodiode for receiving optical signals transmitted through thewaveguide and subsequently converting the optical signals to electricalsignals that are delivered to the interconnect layer. Conversely, inother embodiments, the second device is a sending device, for example,such as a laser for converting electrical signals from the interconnectlayer, for example, to optical signals for transmission to thewaveguide. In the second coupling step 1060, an optical fiber is coupledto the substrate, wherein the optical fiber is configured to interfacewith the waveguide. Optical fibers are typically used in communicationnetworks for the transmission of optical signals between sub mountassemblies and over long distances. By contrast, planar waveguides andthe transmission of optical signals in free space are used to transmitoptical signals within sub mount assemblies and over short distances.Optical fibers that are used to deliver optical signals are typicallyconnected to the substrate and aligned with waveguides or other devices,such as a lens, to provide the necessary interface for transferring theoptical signals from the fiber to the sub mount assembly to which theoptical fiber is connected.

Referring to FIG. 11A, a perspective view of interposer 1100 is shownfor an embodiment that includes inventive dielectric film stack 1140patterned to form a waveguide, a v-groove 1192 for coupling and aligningan optical fiber to the interposer 1100, and x-y-z stop structure 1166for aligning devices to the patterned dielectric stack 1140. In theembodiment shown in FIG. 11A, x-y-z stop structure 1166 is a singleelement. In other embodiments, any one of the x-stop, y-stop, and z stopcan be combined to facilitate the alignment of optical andoptoelectrical devices to the sub mount assembly. In yet otherembodiments, the x-stop, a y-stop, and a z-stop can be in one or moreindividual parts, or multiple parts, to provide the same function ofaligning devices in each of the x, y, and z directions identified inFIG. 11A. In other embodiments, one or more stops are provided for oneof the x, y, and z directions. In yet other embodiments, one or morestops are provided for two or three of the x, y, and z directions. Andin yet other embodiments, multiple stops are provided for one or more ofthe x, y, and z directions. In yet other embodiments, one or morealignment marks are provided in addition to the stops. In yet otherembodiments, alignment marks are provided to align the optical,optoelectrical, and electrical devices without the stops.

Referring to FIG. 11B, a cross sectional schematic of an embodiment forsub mount assembly 1105 is shown that is formed on interconnect layer1120 on substrate 1110 with inventive dielectric stack 1140. In theembodiment shown in FIG. 11B, features 1167, 1168, 1169 are provided forthe alignment of optical or electrical device 1160 to the planarwaveguide fabricated from the dielectric stack 1140. Optoelectricaldevice 1160 is connected through buffer layer 1130 to metal layer 1126.Metal layers 1126 are insulated with intermetal dielectric 1127 ininterconnect layer 1120. In some embodiments, interconnect metal layers1126 connect optoelectrical devices 1160 to integrated electricaldevices 1164 in the substrate 1110 or to other devices in the sub mountassembly 1105. Alignment of optical/optoelectronic device 1160 isrequired to align the optical sending or receiving side 1161 of opticalor optoelectrical device 1160 to the planar waveguide formed from theinventive dielectric stack structure 1140 and to thereby allow for thetransfer of optical signals between the planar waveguide formed from theinventive dielectric stack structure 1140 and the optical oroptoelectrical device 1160. It is important to note that for embodimentsin which the device 1160 is an optical device, alignment is requiredwithin the sub mount assembly 1105 to provide for the transfer ofoptical signals between the planar waveguides and the device 1160 in thesub mount assembly 1105, but not necessarily for electrical connections.In some embodiments, however, metal bond pads are implemented to attachoptical devices 1160. Alignment of the planar waveguides formed from theinventive dielectric stack structure 1140 to optical fiber 1190 isachieved in some preferred embodiments with v-groove 1192 in substrate1110.

In an embodiment shown in FIG. 11B, substrate 1110 is shown withoptional integrated device 1164. Integrated electrical devices 1164, inpreferred embodiments, are connected to the interconnect layer 1120.Interconnect layer 1120 is a structure of metal lines 1126 andintermetal dielectric layers 1127 that provide insulated conductivepathways for interconnecting electrical and optoelectrical devices anddies that are fabricated on, mounted in, or connected from an externalsub mount assembly to the sub mount assembly 1105. In preferredembodiments in which optoelectrical die 1160 are mounted onto the submount assembly 1105, metal interconnects 1126 are routed within theinterconnect layer 1120 to provide electrical connections for electricaland optoelectrical devices in, on, or connected to the sub mountassembly 1105, and to the underlying electrical devices 1164.

Alignment marks 1165 are provided in some preferred embodiments for thealignment of optical, electrical, and optoelectrical devices on the submount assembly 1105. In some embodiments, alignment marks are providedin the buffer layer 1130 or the top layer of the interconnect layer 1120of the interposer 1100 for alignment of devices, such as theoptoelectrical device 1160, within the sub mount assembly.Alternatively, alignment marks can be provided in other layers, on orin, the substrate. In preferred embodiments, alignment mark 1169 is foroptical alignment, as is used in automated die placement tools forexample, to position the die onto the sub mount assembly 1105. Alignmentmark 1169 in embodiments is a patterned feature in or on a layer or thesubstrate in the sub mount assembly 1105. In some embodiments, thepatterned features are an ink mark, a coloration mark, or discolorationmark of the top or another layer in the substrate or in one of thelayers on the substrate. In some embodiments, the alignment mark is ameans of providing optical contrast. Alignment mark 1169 in someembodiments is one or more of an etched feature, a deposited feature, alaser scribed feature, a feature created by exposure to an electronbeam, or an ion milled feature.

Alignment features 1167 and 1168 provide physical stops for thealignment of optical die 1160, and other devices on the sub mountassembly 1105. Accurate placement of devices and waveguides on opticalsub mount assemblies is necessary for the transmission of the opticalsignals through the optical circuit on the sub mount assembly 1105. Ininstances for which optical devices and features are not aligned,significant loss of the optical signal can occur, and in extremecircumstances can result in complete loss or blockage of the opticalsignal. Stop 1168, in the embodiment shown in FIG. 11B, is a z-directionstop, in that this stop is intended to fix the height (in thez-direction) of optoelectric device 1160 on the sub mount assembly 1105.Stop 1167, also in the embodiment shown in FIG. 11B, is an x-directionstop, in that this stop is intended to fix the location of theoptoelectric device 1160 in the x-direction as referenced in FIG. 11A onthe sub mount assembly 1105. In some embodiments, a y-direction stop isalso included. And in yet other embodiments, one or more of anx-direction stop, a y-direction stop, and a z-direction stop areprovided. In yet other embodiments, one or more stops are provided foreach device 1160 mounted on the sub mount assembly 1105 that requiresalignment.

Additionally, in preferred embodiments, a v-groove feature 1192 or otheralignment feature is provided to align the optical fiber 1190 to the submount assembly 1105 and to planar waveguides formed from the inventivedielectric stack 1140.

Referring to FIG. 12, steps for forming a dielectric interposer with apatterned waveguide from the inventive dielectric stack structure areshown that include a providing step 1200, a first forming step 1210, asecond forming step 1220, and a third forming step 1230 as describedherein. In providing step 1200, a substrate is provided wherein thesubstrate includes an interconnection layer (see interconnect layer1120, for example.) In a first forming step 1210, a waveguide is formedthat includes the inventive dielectric film structure on the substrate.In a second forming step 1220, at least one of an x-stop, a y-stop, az-stop, and an alignment mark are formed on the substrate wherein thex-stop, a y-stop, a z-stop, and an alignment mark are configured toalign a device with the waveguide. In a third forming step 1230, atleast one alignment feature is formed on the substrate wherein thealignment feature is configured to align an optical fiber with thewaveguide.

A specific benefit and feature of the planar dielectric waveguidestructure is that in addition to its primary use for fabricating opticalwaveguides, it can also be used to produce mechanical features such asthe alignment stops. In some embodiments, for example, the inventivedielectric stack is patterned using photoresist, for example, and thenetched to a depth to establish the z-direction height, and for example,to create features for x-direction and y-direction stops as required.The capability to produce stops from the dielectric stack material,outside of the waveguide areas, provides an added benefit inimplementing the planar dielectric stack structure on the inventiveinterposer. The use of the dielectric stack film stack to producemechanical features such as the structures described for alignment stopsand marks, as well other features described herein, is particularlyenabled by the achievable thickness ranges of the inventive dielectricstacks. Thicknesses on the order of 2-25 micrometers are of the samethickness ranges that are suitable for alignment marks and stops. Bycombining the highly accurate vertical dimensioning capability that isachievable with highly controllable additive deposition technology withthe highly controllable subtractive dry and wet etch technology, therelative heights of alignment features and stop features formed from thedielectric stack film structures can be formed with high accuracy. Inaddition to the applicable thickness benefits, the accuracy in thelateral dimensioning of the stops is generally provided byphotolithographic patterning processes, which are highly accurate towithin small fractions of a micrometer.

Referring to FIG. 13A, sub mount assembly 1305, formed from interposer1300, is shown that includes substrate 1310, interconnect layer 1320,and inventive dielectric stack 1340. Dielectric stack 1340 is patternedto form inventive planar dielectric waveguide. Interconnect layer 1320is a structure of metal lines 1326 and intermetal dielectric 1327. Metallines 1326 provide electrically conductive pathways for interconnectingelectrical and optoelectrical devices and dies that are fabricated on,mounted in, or connected from an external sub mount assembly to thedielectric interposer 1300. In a preferred embodiment, one or moreoptoelectrical die 1360 are mounted onto the interposer 1300, and themetal interconnects 1326 are routed within the interconnect layer 1320to provide electrical connections for electrical and optoelectricaldevices in, on, or connected to the interposer 1300, or sub mountassembly 1305, and to underlying integrated electrical devices in thesubstrate, if present. It is to be understood that optical devices canbe mounted with metal bond pads 1322, as means for mechanical bonding,without the specific requirement for electrical connections to otherdevices on the sub mount assembly 1305. A discrete waveguide (see 940,for example) may not require electrical interconnection to other deviceson the sub mount assembly 1305, but the same or similar bondingmethodologies that are used for to provide mechanical bonding andelectrical interconnection can be utilized to bond the optical device1360 to the sub mount assembly 1305.

In optical circuits, and in particular, in optical circuits within whichlasers are utilized for converting electrical signals to opticalsignals, significant levels of heat can be generated that may requiredissipation in some embodiments to prevent premature failure of, ordamage to, a sub mount assembly or components mounted on the sub mountassembly. In addition to lasers, other optical, electrical, andoptoelectrical devices can generate significant levels of heat while inoperation. Submount assemblies, therefore, in some embodiments, wouldbenefit from design features that facilitate heat dissipation. In theinventive sub mount assembly 1305, one or more of a thermally conductivedielectric layer is incorporated into the inventive sub mount assembly1305 with the inventive dielectric stack 1340 to facilitate dissipationof thermal energy from the sub mount assembly 1305.

In the cross section shown in FIG. 13A of an embodiment for theinventive sub mount assembly 1305, a thermally conductive dielectriclayer 1328 is disposed between the substrate 1310 and the interconnectlayer 1320. In these and other embodiments, the thermally conductivedielectric material, such as aluminum nitride, for example, is combinedwith inventive sub mount assembly 1305 in conjunction with heatgenerating optoelectrical devices 1360 and inventive planar dielectricstack 1340. In embodiments, inclusion of heat-dissipating, thermallyconductive dielectric layer 1328 with inventive dielectric stackstructure 1340 improves the reliability of the sub mount assembly 1305by providing thermally conductive pathways that allow for thetransferring of heat from heat generating devices 1360 to heat sinksconnected to the substrate 1310 or the sub mount assembly 1305. Inpreferred embodiments, thermally conductive dielectric layer 1328 isaluminum nitride or an alloy of aluminum nitride. In other embodiments,other thermally conductive dielectric material is used in sub mountassembly 1305 in conjunction with the optoelectrical devices 1360 andinventive planar dielectric stack 1340. In other embodiments, materialsthat are electrically conductive, such as the metal traces 1326 that areused in the interconnect layer 1320, are used to transfer heat from heatgenerating devices 1360 to the thermally conductive layers 1328 forconduction of heat to heat sinks on the sub mount assembly 1305.

In other embodiments, as for example shown in FIG. 13B, a thermallyconductive dielectric layer 1329 is positioned within the interconnectlayer 1320. The metal traces 1326 in interconnect layer 1320, which arecommonly composed of aluminum, copper, other metal, or combination ofmetals, generally have a high thermal conductivity, and can provide heatdissipation pathways from the heat generating optoelectronic device 1360to the thermally conductive dielectric material 1329. The thermallyconductive dielectric material 1329 is used in some embodiments toprovide pathways that allow for the transferring of heat from the heatgenerating devices 1360 to one or more heat sinks connected to the submount assembly 1305.

Referring to FIG. 14A, a sequence of steps for forming a substrate witha thermally conductive layer and an interconnection layer used inembodiments of the inventive dielectric interposer 1300 is shown. Thesesteps, which include the formation of a thermally conductive layer areshown that include a providing step 1400, a first forming step 1410, anda second forming step 1420, as described herein. In providing step 1400,a substrate is provided whereon a thermally conductive layer is formedin first forming step 1410. In the second forming step 1420, aninterconnection layer is formed on the thermally conductive layer. Thesequence of steps shown in FIG. 14A is one method for preparing asubstrate with a thermal layer 1380 and an interconnect layer 1320 inpreparation for the deposition of the inventive dielectric stack 1340,and the resulting formation of the inventive dielectric interposer 1300.In embodiments, the thermal layer 1328 is a heat sink for the removal ofexcess heat from devices 1360, for example. In other embodiments, thethermal layer 1328 provides a thermally conductive pathway for thetransfer of heat from heat-generating devices 1360 to heat sinks on orconnected in some way to the sub-mount assembly 1305.

In FIG. 14B, steps for forming other embodiments of the inventivedielectric interposer 1300 with a thermally conductive dielectric layerare shown. The steps in FIG. 14B include a providing step 1440, a firstforming step 1450, a second forming step 1460, and a third forming step1470. In providing step 1440, a substrate 1310 is provided for thedielectric interposer 1300. In first forming step 1450, a whole or partof an interconnect layer is formed on the substrate 1310. In someembodiments, first forming step 1450 includes the formation of a part ofthe interconnect layer, that is, one or more layers of the interconnectlayer 1320 but not the complete thickness of the interconnect layer. Inother embodiments the thermally conductive dielectric layer 1329 isformed on the interconnect layer 1320. It is important to note that thethermally conductive layer can be formed at one or more of variouspositions in the interposer structure 1300 and remain within the scopeof the current invention. Embodiments for the thermally conductivedielectric layer, for the purposes of providing a heat sink or a pathwayto a heat sink include one or more of a thermally conductive layer 1328on the substrate 1310, a thermally conductive layer 1329 on theinterconnect layer 1320, and a thermally conductive layer 1329 withinthe interconnect layer 1320, as described herein. The thermallyconductive layer, in some embodiments, is partially at one height in theinterconnect layer 1320, and is partially at one or more other heightsin the interconnect layer 1320. For example, a thermally conductivelayer 1328 may be on the substrate 1310 for part of the sub mountassembly 1305 and then partially at another height within theinterconnect layer 1320. In these embodiments, connections between thelevels of the thermally conductive layers can be provided using the samethermally conductive material as in the thermally conductive layers1329, a metal layer 1326, or an intermetal dielectric 1327. In preferredembodiments, the use of the same thermally conductive material toconnect multiple thermally conductive layers 1328, 1329 is expected toproduce the most efficient heat transfer although this approach mightalso have increased processing costs in some embodiments.

The second forming step 1460, for embodiments in which the thermallyconductive layer 1329 is formed within the interconnect layer 1320, istypically followed by completion of the remaining layers of theinterconnect layer 1320. In these embodiments, electrical connections1326 may be required in some embodiments through the thermallyconductive dielectric layer 1329 to connect underlying integratedelectrical devices (see integrated device 764, for example) or toconnect underlying connection layers 1326 that reside below thethermally conductive layer 1329. Third forming step 1470 includes theforming of an electrical connection in or through the dielectric layerthat contains a thermally conductive dielectric layer 1329 to one ormore of the interconnection layers 1326 that reside in the dielectriclayer and in some embodiments to underlying integrated electricaldevices (see integrated electrical device 764, for example). Similarly,for embodiments in which the thermally conductive layer 1329 isdeposited on the complete, or partially completed, interconnect layer1320, third forming step 1470 also includes the forming of electricalconnections 1326 through the thermally conductive dielectric layer 1329and the forming of one or more connections in or through this thermallyconductive layer 1329 to one or more of the interconnection layers 1326that reside below the thermally conductive dielectric layer 1329. Inembodiments in which the interconnect layer 1320 is nearly completed,the thermally conductive layer 1329 may form the uppermost dielectriclayer in the structure of the interconnect layer 1320.

It is important to note that the thermally conductive layer 1328, 1329can be incorporated into the inventive interposer 1300 in various waysand remain within the scope of the current invention. FIG. 14B showssteps in the formation of some embodiments of the inventive dielectricinterposer 1300 with the inventive dielectric stack 1340 for which athermally conductive dielectric layer 1328, 1329 is included asdescribed herein. In embodiments, the thermally conductive dielectriclayer 1328, 1329 is one or more of a heat sink for the removal of excessheat from devices 1360, for example, and a thermally conductive pathwayfor the transfer of heat from heat-generating devices 1360 to heat sinkson or connected to the sub-mount assembly 1305. The combination ofheat-removing layers 1328, 1329 with the heat generating devices 1360and integrated planar dielectric waveguides formed from the inventivedielectric stack structure 1340 are beneficial for enhancing thereliability of sub mount assemblies that are uniquely enabled by thiscombination.

Referring to FIG. 15A, a cross sectional schematic of an unpatternedinventive dielectric stack 1540 is shown for embodiments of theinventive dielectric interposer 1500 formed on substrate 1510 forembodiments with optional thermally conductive layer 1528, interconnectlayer 1520, and buffer layer 1530. Patterning of inventive dielectricstack 1540 from FIG. 15A yields inventive dielectric stack section 1540a and inventive dielectric stack section 1540 b as shown in thecross-sectional schematic in FIG. 15B. In preferred embodiments,dielectric stack section 1540 a and dielectric stack section 1540 b formcavity 1594. The inset in FIG. 15B shows a perspective view of the topsurface of inventive interposer 1500 after patterning of the dielectricstack 1540 to form dielectric stack sections 1540 a, 1540 b, and thecavity 1546.

Referring to FIG. 15C, a schematic cross section of inventive dielectricinterposer 1505 is shown with optoelectrical device 1560 within cavity1594. In some embodiments, the optoelectrical device 1560 is connectedwith bond pad 1522 to the underlying metallization 1526 in theinterconnect layer 1520 through openings in buffer layer 1530.Metallization traces 1526 generally form interconnections between thevarious electrical devices on and within the interposer and are shownfor general demonstrative purposes in FIG. 15, and in other figures, andnot intended to show a specific patterns or structures for theinterconnections. Metallization layers 1526 provide interconnectionsbetween electrical and optoelectrical devices mounted onto theinterposer 1500, to integrated electrical devices in the substrate (seeintegrated electrical device 764, for example), and to other devices andother sub mount assemblies connected to sub mount assembly 1505.

In FIG. 15D, a cross sectional schematic of cap 1596 on sub mountassembly 1505 to create capped optoelectronic package 1508 is shown. Insome embodiments, cap 1596 is provided to seal the cavity 1594, and toprovide hermetically sealed protection of the sub mount assembly withinthe cavity 1594. Cap 1596 is coupled to the cavity walls formed fromdielectric stack sections 1540 a, 1540 b, formed from the inventivedielectric stack structure 1540, to cover and protect the optoelectricdevices 1560 mounted within the cavity 1546. In typical preferredembodiments, a metal seal 1597 is utilized to bond the cap 1596 to thecavity walls 1540 a, 1540 b. In other embodiments, the seal or bondlayer 1597 between the cap 1596 and the mechanical supports can be madefrom materials such as adhesive resins, solder material, and the like.The cap 1596 is shown mounted directly on the inventive dielectric stackstructure 1540, but it should be understood that additional layers canbe formed above the dielectric stack structure 1540 for various reasonsthat include one or more of improved bonding layer adhesion, verticalheight adjustment, alignment, and provision for positional stops, amongother reasons, and remain within the scope of the current invention.

In FIG. 16, the steps for providing a capped sub mount assembly 1508from inventive sub mount assembly 1505 using inventive dielectric stackstructure 1540 are shown and include a providing step 1600, a firstforming step 1610, a first patterning step 1620, a second forming step1630, and a third forming step 1640 as described herein for someembodiments. In the providing step 1600, a substrate 1510 that includesan interconnection layer 1520 is provided. In some embodiments, thesubstrate 1510 has a thermally conductive layer 1528 on substrate 1510or within the interconnect layer 1520. In some other embodiments, thesubstrate 1510 does not have a thermally conductive layer 1528 on or insubstrate 1510, or on or within the interconnect layer 1520. In a firstforming step 1610, inventive dielectric stack 1540 is deposited onto theinterconnect layer 1520. Inventive dielectric stack 1540 is patterned infirst patterning step 1620 to form a waveguide from the inventivedielectric stack 1540 and one or more support structures 1540 a and 1540b that are also formed from the inventive dielectric stack 1540. Anembodiment of support structures is shown for example in FIGS. 15B-D. Ina second forming step 1630, a device 1560, for example, is formed on thesubstrate, wherein the device is configured to couple to the waveguideformed from the dielectric stack 1540. In the third forming step 1640, acap 1596 is positioned to cover the device that is coupled to thewaveguide, by disposing the cap 1596 on the dielectric stack structure1540 patterned to form a waveguide 1540 a, which also serves as amechanical support structure, and the support structures 1540 b. Thebenefit of using the inventive dielectric stack as both a mechanicalsupport and a waveguide enables the use of the waveguide to transmitlight signals into the cavity and out from devices mounted within thecavity while providing a capability for hermetic sealing. Thetransmission of light through planar waveguides formed from theinventive dielectric film structures 1540 can be used to facilitate thetransmission or receiving, or both, of optical signals from opticalfibers mounted external to the cavity, through the cavity walls 1540 a,to or from devices 1560 mounted within the cavity 1594.

In the cross sections of the embodiments for the inventive interposersand sub mount assemblies shown and described herein, it should beunderstood that waveguides fabricated from inventive dielectric stack140, 540, 740, 840, and 940, in some embodiments can be a small sectionof waveguide aligned to an optical or electrical device, for example,for the transmission of optical signals to and from an optical fiberconnected to the sub mount assembly. In other embodiments, thesewaveguides can include sections of the inventive dielectric stack 140that are patterned spot size converters, filters, arrayed waveguides,multiplexers, demultiplexers, gratings, power combiners, and the like.In yet other embodiments, these waveguides can provide part of amechanical structure for the formation of hermetic seals. In yet otherembodiments, theses waveguides can be a combination of one or more ofthese types of structures fabricated from the inventive dielectric stackstructure 140. In yet other embodiments, the buffer layer and the layersof the repeated stack are patterned to form a filter, an arrayedwaveguide, a grating, a multiplexer, a demultiplexer, a spot sizeconverter, or a power combiner.

The foregoing disclosure of the exemplary embodiments of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many variations andmodifications of the embodiments described herein will be apparent toone of ordinary skill in the art in light of the above disclosure. Thescope of the invention is to be defined only by the claims appendedhereto, and by their equivalents.

Further, in describing representative embodiments of the presentinvention, the specification may have presented the method and/orprocess of the present invention as a particular sequence of steps.However, to the extent that the method or process does not rely on theparticular order of steps set forth herein, the method or process shouldnot be limited to the particular sequence of steps described. As one ofordinary skill in the art would appreciate, other sequences of steps maybe possible. Therefore, the particular order of the steps set forth inthe specification should not be construed as limitations on the claims.In addition, the claims directed to the method and/or process of thepresent invention should not be limited to the performance of theirsteps in the order written, and one skilled in the art can readilyappreciate that the sequences may be varied and remain within the spiritand scope of the present invention.

What is claimed is:
 1. A waveguide comprising a buffer layer comprisingSiON on a substrate, wherein a functionality of the substrate issusceptible to be degraded at temperatures greater than 400 C; arepeated stack of two or more SiON layers on the buffer layer, whereinthe two or more layers comprise at least two layers having differentindexes of refraction, wherein the waveguide comprising the buffer layerand the layers of the repeated stack are functionally formed attemperatures less than or equal to 400 C.
 2. A waveguide as in claim 1wherein the buffer layer and the layers of the repeated stack functionas a waveguide after being formed at temperatures less than or equal to400 C.
 3. A waveguide as in claim 1 wherein the processes to completelyform the waveguide are limited to temperatures less than or equal to 400C.
 4. A waveguide as in claim 1 wherein the substrate comprises amaterial or an element that has a property changed at temperaturesgreater than 400 C, or wherein the substrate comprises an interconnectlayer that is susceptible to be damaged at temperatures greater than 400C.
 5. A waveguide as in claim 1 wherein the substrate comprises a devicefabricated thereon, wherein the device or a connection element connectedto the device is susceptible to be damaged at temperatures greater than400 C.
 6. A waveguide as in claim 1 wherein the buffer layer and thelayers of the repeated stack comprise a stress having a magnitude lessthan or equal to 20 MPa.
 7. A waveguide as in claim 1 wherein the bufferlayer and the layers of the repeated stack comprise a stoichiometry ofSi, O, and N to provide a stress having a magnitude less than or equalto 20 MPa.
 8. A waveguide as in claim 7 wherein the stoichiometry isconfigured to provide an index of refraction between 1.45 and 2.15 orbetween 1.6 and 2.05.
 9. A waveguide as in claim 1 wherein the bufferlayer is thicker than or equal to 4 microns.
 10. A waveguide as in claim1 wherein the repeated stack comprises 3 to 20 repeated pairs of SiONlayers.
 11. A waveguide as in claim 1 further comprising at least one ofone or more SiON bottom spacer layers disposed on the buffer layer, oneor more SiON top spacer layers disposed on the repeated stack, or a SiONtop layer disposed on the repeated stack.
 12. A waveguide as in claim 1wherein the overall total thickness of the repeated stack is between 8and 12 microns for a direct optical coupling with an optical fibercable.
 13. A waveguide comprising a buffer layer comprising SiON; arepeated stack of two or more SiON layers, wherein the two or morelayers comprise layers having different indexes of refraction, whereineach layer of the buffer layer and the layers of the repeated stackcomprises a stoichiometry of Si, O, and N to provide a stress having amagnitude less than or equal to 20 MPa.
 14. A waveguide as in claim 13wherein the stoichiometry is configured to provide an index ofrefraction between 1.45 and 2.15 or between 1.6 and 2.05.
 15. Awaveguide as in claim 13 wherein the buffer layer is thicker than orequal to 4 microns.
 16. A waveguide as in claim 13 wherein the repeatedstack comprises 3 to 20 repeated pairs of SiON layers.
 17. A waveguideas in claim 13 wherein the overall total thickness of the repeated stackis between 8 and 12 microns for a direct optical coupling with anoptical fiber cable.
 18. A waveguide comprising a buffer layercomprising SiON on a substrate; a repeated stack of two or more SiONlayers on the buffer layer, wherein the two or more layers comprise atleast two layers having different indexes of refraction, wherein thesubstrate comprises a groove configured to fit an optical fiber cablefor interfacing with the waveguide, wherein the overall total thicknessof the repeated stack is between 8 and 12 microns for a direct opticalcoupling with the optical fiber cable.
 19. A waveguide as in claim 18wherein the layers of the repeated stack comprise a stoichiometry of Si,O, and N to provide a stress having a magnitude less than or equal to 20MPa.
 20. A waveguide as in claim 19 wherein the stoichiometry isconfigured to provide an index of refraction between 1.45 and 2.15 orbetween 1.6 and 2.05.